Up-regulation of intercellular adhesion molecule-1 (ICAM-1), endothelial leucocyte adhesion molecule-1 (ELAM-1) and class II MHC molecules on pulmonary artery endothelial cells by antibodies against U1-ribonucleoprotein

Abstract

In order to elucidate the pathogenic role(s) of autoantibodies in connective tissue disease (CTD), we examined whether autoantibodies against U1-ribonucleoprotein (RNP) and double-stranded (ds) DNA can up-regulate ICAM-1, ELAM-1 and class I and II MHC molecule expression on pulmonary artery endothelial cells (HPAEC). ICAM-1, ELAM-1 and class II MHC molecule expression on HPAEC cultured in the presence of anti-U1-RNP-containing and anti-dsDNA-containing IgG from CTD patients was up-regulated significantly in comparison with that on HPAEC cultured with IgG from normal healthy volunteers. Affinity chromatographic enrichment and depletion of the anti-U1-RNP antibody content of anti-U1-RNP-containing IgG confirmed that the anti-U1-RNP antibody did up-regulate ICAM-1, ELAM-1 and class II MHC molecule expression. The finding that an IgG F(ab')2-purified anti-U1-RNP antibody also up-regulated expression of these molecules may indicate that mechanisms other than Fc receptor-mediated stimulation are involved. These in vitro findings suggest that autoantibodies against U1-RNP and dsDNA play important roles in the immunopathological processes leading to the proliferative pulmonary arterial vasculopathy observed in CTD patients with pulmonary hypertension by up-regulating adhesion and class II MHC molecule expression on endothelial cells.

Fig 1

Expression of adhesion (ICAM-1 and ELAM-1) and MHC (class I and II) molecules on pulmonary artery endothelial cells (HPAEC) incubated with various concentrations of rIL-1α. Bars show the mean ± s.d. of quadruplicate experiments.

Fig 2

(See next page) Expression of adhesion and MHC molecules on pulmonary artery endothelial cells (HPAEC) incubated with various concentrations of anti-U1-RNP⁺ (n = 19), anti-dsDNA⁺ (n = 19) and control (n = 10) IgGs. The addition of 200 μg/ml anti-U1-RNP⁺ and anti-dsDNA⁺ IgGs to HPAEC significantly up-regulated the expression of ICAM-1 (a, P < 0.001 and P < 0.01, respectively), ELAM-1 (b, P < 0.001 and P < 0.01, respectively), and class II MHC molecule (d, P < 0.05 and P < 0.05, respectively) compared with the levels expressed by HPAEC incubated with 200 μg/ml control IgG. Class I MHC molecule expression (c) on HPAEC was up-regulated neither by anti-U1-RNP⁺ nor anti-dsDNA⁺ IgGs.

Fig 3

Expression of adhesion and MHC molecules on pulmonary artery endothelial cells (HPAEC) incubated with various concentrations of purified anti-U1-RNP and anti-U1-RNP-depleted IgG. Purified anti-U1-RNP, but not anti-U1-RNP-deleted IgG, up-regulated ICAM-1 (a), ELAM-1 (b) and class II (d) MHC molecule expression on HPAEC in a concentration-dependent manner. Class I MHC molecule expression (c) on HPAEC was up-regulated neither by purified IgG anti-U1-RNP nor by anti-U1-RNP-depleted IgG. **P < 0.01; *P < 0.05 compared with adhesion and MHC molecule expression on HPAEC incubated with corresponding concentrations of anti-U1-RNP-depleted IgG.